Los Angeles, California – It's been just over three years since the family of actor Bruce Willis made his dementia diagnosis public. In the meantime, the Hollywood star's has reportedly deteriorated significantly.

An insider revealed that Willis has experienced a significant mental decline. The personality of the 71-year-old Die Hard star is also said to have changed, according to the Daily Mail.

Three years after being diagnosed with frontotemporal dementia, Willis has "declined a lot mentally."

He is reportedly living more and more "in his own world."

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"Sometimes he looks like a baby who is staring at an object with curiosity, just taking it in," a source said about Willis' condition.

Yet outwardly, he still looks to be a "healthy middle-aged man."

The acting legend himself is apparently unaware of his ongoing mental decline. While Willis knows his life has changed dramatically, he cannot grasp the full extent of his illness.

The action star doesn't complain about his condition – another sign that his personality has already changed. He used to be energetic and talkative, but now he's noticeably calmer and more relaxed, according to insiders.

His wife, Emma Heming‑Willis, made it clear in September how taxing the illness is for the whole family. In an interview, she described it as a constant "state of grief" while caring for her husband.